1. Field of the Invention
The invention relates to a fuel injection control apparatus for a direct injection type internal combustion engine in which fuel is injected directly into the combustion chamber.
2. Description of the Related Art
In a direct injection type internal combustion engine, if the fuel injected from an injector is not sufficiently atomized, a large amount of fuel adheres to the inner surface of the cylinder, and the fuel is mixed into lubricating oil. As a result, the lubricating oil is diluted with the fuel, also known as “fuel dilution”.
Therefore, fuel injection control apparatuses that estimate the degree of such fuel dilution have been proposed. For example, Japanese Patent Application Publication No. 2003-322044 A discloses a fuel injection control apparatus which estimates that the degree of fuel dilution has increased, when an accumulated value such as an intake air amount accumulated value, which indicates an amount of air taken in an internal combustion engine from the time the internal combustion engine starts until it stops, is equal to or less than a reference value.
Dilution of lubricating oil with fuel greatly influences the amount of fuel supplied to the combustion chamber. Accordingly, the degree to which lubricating oil has been diluted with the fuel needs to be estimated accurately, and the estimated degree of dilution needs to be taken into account when the fuel injection control is performed.
The fuel injection control apparatus disclosed in Japanese Patent Application Publication No. 2003-322044 A estimates the degree of fuel dilution based only on the intake air amount accumulated value. With such a fuel injection control apparatus, it is difficult to obtain estimated results having sufficiently high accuracy.